A transfer device can be arranged in an injection valve of an internal combustion engine and transfers the displacement of the actuator to a needle valve. Piezoactuators, which, because of their very fast reaction to control signals are very suitable for precisely controlling the dosing of fuel and if necessary allowing several consecutive part injections during an operating cycle of a cylinder of the internal combustion engine, are used ever more frequently as actuators.
The fuel pressure in an injection valve for diesel combustion engines amounts to up to 2,000 bar. The result of this is that considerable forces have to be applied for opening or closing the injector needle. Furthermore an actuator embodied as a piezoactuator only has a far smaller lift than the lift of the injector needle required. The provision of a transfer device for transferring lift of the actuator is known, said device amplifying the lift and/or also creating a temperature-related length equalization.
A fuel injection valve is known from DE 199 50 760 which features a piezoelectric or magnetostrictive actuator. A transfer device with two lifting plungers displaceable against each other is provided between the actuator and a valve needle. The transfer device is hermetically sealed in relation to an inner valve space. The first lifting plunger is effectively connected to the actuator and has an open cylindrical shape on one side, the opening of which is arranged facing away from the actuator. The second lifting plunger is guided in the cylindrical opening. The first lifting plunger is in its turn located in a hollow cylindrical housing. A transfer chamber is embodied between an end surface of the housing and the first and the second plunger. Furthermore a tensioning spring is provided which pre-tensions the first and second plunger in opposite directions. Furthermore a compensating chamber is provided which is partly delimited by a corrugated tube and is hydraulically coupled to the transfer chamber. The compensating chamber is used to compensate for the change in volume of the transfer chamber and to supply the transfer chamber with a transfer medium at a defined pressure. This type of corrugated pipe is relatively complex and expensive however.
A transfer device for transmission of the displacement of a piezoelectric actuator of an injection valve is also known from DE 101 62 045 A1. The actuator acts on a first lifting plunger 1 which in part of its area is embodied in the form of a cylindrical pot and in the inside of which a second plunger engages which is coupled to a servo valve or an injector needle of the injection valve. The first lifting plunger is guided in a cylinder body. Likewise the second lifting plunger is guided in the cylinder body. The first and the second lifting plungers are coupled via a pressure chamber. An axial displacement of the first lifting plunger is transmitted by means of the pressure chamber into an opposite axial displacement of the second lifting plunger. Furthermore a compensating chamber is provided which compensates for the change in volume in the transfer chamber and supplies the transfer chamber with a transfer medium at a defined pressure.